According to a conventional induction heating cooker, a plurality of electrodes are provided around an outer periphery of a heating coil and the boiling over is sensed based on a change in electrostatic capacitance of the electrodes as described in Unexamined Japanese Patent Publication No. 2008-159494 (Patent Literature 1).
FIG. 7 is a view showing a configuration of the conventional induction heating cooker disclosed in Patent Literature 1. FIG. 8 is a graph showing a change in electrostatic capacitance in the electrodes used for sensing the boiling over described in Patent Literature 1.
As shown in FIG. 7, the conventional induction heating cooker is provided with a drive circuit 102 for inputting a low-frequency power from an AC power supply 101 and supplying a high-frequency power to a heating coil 104 to heat a cooking container (not shown) by induction. In addition, a plurality of electrodes 103 each having a shape of a small circular plate are concentrically dispersed around the outer periphery of the heating coil 104. Each of the dispersed electrodes 103 is connected to an electrostatic capacitance measuring circuit 106. The electrostatic capacitance measuring circuit 106 detects electrostatic capacitance between the electrode 103 and the electrostatic capacitance measuring circuit 106. Hereinafter, this electrostatic capacitance is simply referred to as “electrostatic capacitance of the electrode 103”. The electrostatic capacitance of the electrode 103 depends on arrangements of a dielectric body (such as a top plate) and a conductive body (such as a metal cooking container or the heating coil 104) provided around the electrode 103. According to the conventional induction heating cooker configured as described above, after liquid has boiled over from an edge part of the cooking container such as a pan set on the heating coil 104 with the top plate interposed between them, the spilt liquid exists on any of the electrodes 103 or in a neighborhood of it. When the spilt liquid exists, the electrostatic capacitance of any of the electrodes 103 increases. The boiling over is sensed by sensing the increase in electrostatic capacitance. When the boiling over occurs on the any of the electrodes 103 or in the neighborhood of it, water exists between the electrode 103 and the cooking container or the heating coil 104, so that the electrostatic capacitance between the heating coil 104 and the electrode 103 abruptly increases. Therefore, the boiling over can be sensed by sensing the electrostatic capacitance of the electrode 103 as described above.
According to the conventional induction heating cooker, when the phenomenon that the electrostatic capacitance of the electrode 103 abruptly increases is detected (refer to FIG. 8), the control circuit 105 determines it as the boiling over, and stops an action of the drive circuit 102, or reduces the high-frequency current flowing to the heating coil 104.
PLT 1: Unexamined Japanese Patent Publication No. 2008-159494